Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$78.96	13.258%	$89.4285	$89.43	$89.45	$89.40
Purchase #2	$75.79	5.841%	$80.2169	$80.22	$80.20	$80.20
Purchase #3	$231.50	4.381%	$241.642	$241.64	$241.65	$241.60
Purchase #4	$89.63	3.432%	$92.7061	$92.71	$92.70	$92.70
Purchase #5	$99.60	4.772%	$104.3529	$104.35	$104.35	$104.40
Purchase #6	$103.46	13.350%	$117.2719	$117.27	$117.25	$117.30
Purchase #7	$88.85	10.758%	$98.4085	$98.41	$98.40	$98.40
7 purchase totals =	$767.79		$824.0268	$824.03	$824.00	$824.00